A filter assembly of the type generally contemplated by the present invention is preferably adapted for pressure filtration in industrial applications while being designed to separate solid contaminants from working liquids in many different applications including, for example, metal-working coolants, food-processing liquids, chemicals and hazardous wastes.
The filter assembly typically comprises a vertical or horizontal stack of filter plates including a lower filter plate and an upper filter plate, one of which is mounted to a rigid structure or frame, called the filter press, and a variable number of intermediate filter plates, movably mounted to the fixed plate or filter press, between the upper and lower plates. The filter plates are typically large and may weigh up to several hundred pounds each. A layer of filter media, usually provided in long sheet-like rolls, is placed between each pair of filter plates. Each pair of filter plates, together with the filter media therebetween, forms dirty and clean compartments. The dirty compartment receives dirty, contaminated liquid under pressure which is thus forced through the filter media, thereby depositing the filter cake solids (contaminants with or without a filter aid) on the filter media. The resultant clean, filtered liquid enters the clean compartment of the adjacent plate.
In certain filtration applications, such as in the treatment of metal-rolling coolants and some food processes, it is necessary to remove from the liquid, contaminants as small as 0.5 microns (0.5 millionths of a meter). This level of filtration frequently requires the filter media discussed above to be supplemented with the addition of filter aids in the form of diatomaceous earth and/or Fuller's earth, or other similar products. These filter aids create a filter cake on the filter media which facilitates separation of the super-fine particles and color bodies from the liquid to further purify the working liquid in the filter assembly.
The use of filter aids is discussed herein since, when the filter aids are used, they combine with impurities from the dirty liquid to form a filter cake deposited upon the filter media. As noted above, filter assemblies of the type contemplated by the present invention are adapted for retrieval of the spent filter media and it is desirable to first separate the filter solids from the filter media. Otherwise, the use of filter aids and the manner in which they are selected and introduced into the filter system are not within the scope of the present invention and accordingly are not discussed in greater detail herein.
Filter assemblies including filter stacks with multiple filter chambers or compartments and employing filter media for separating solid contaminants from a dirty liquid have been disclosed for example in U.S. Pat. No. 4,274,961 issued Jun. 23, 1981 to Hirs; U.S. Pat. No. 4,289,615 issued Sep. 15, 1981 to Schneider, et al. and U.S. Pat. No. 4,362,617 issued Dec. 7, 1982 to Klepper.
The Schneider, et al. and Klepper references noted above also disclose and discuss representative "extractor devices" for use in filter stack assemblies.
U.S. Pat. No. 4,869,834 issued Sep. 26, 1989 to Hudson discloses yet another similar filter assembly as in the above references while also disclosing additional roller means for rewinding or collecting the spent filter media after it is extracted from the filter chambers in the filter stack assembly.
The reference noted immediately above also discussed the use of so-called "deflection edges" (or rollers for changing the filter media path of travel for the stated purpose of avoiding skewing of the filter media as it travels through the filter assembly).
The above noted references are believed representative of a relatively wide number of other prior art references disclosing generally similar filter assemblies. Accordingly, the above noted references are believed to be generally representative of the prior art.